1. Field of the Invention
The present invention relates to an electron-emitting device having a lanthanum boride layer and a display panel.
2. Description of the Related Art
In a general field-emission-type electron-emitting device, a voltage is applied between an electron-emitting member and a gate electrode to generate a strong electric field at the tip of the electron-emitting member, allowing the electron-emitting member to emit electrons into a vacuum.
In such a field-emission-type electron-emitting device, the electric field strength used for electron emission greatly depends on the work function of the surface of an electron-emitting member and its tip shape. It is theoretically believed that an electron-emitting member having a lower surface work function can emit electrons in a weaker electric field.
Japanese Patent Laid-Open No. 01-235124 and U.S. Pat. No. 4,008,412 disclose an electron-emitting device that has a surface layer formed of a low-work-function material, lanthanum hexaboride (LaB6), on a tungsten or molybdenum emitter.
Japanese Patent Laid-Open No. 07-078553 discloses a field-emission microcathode.
A large number of field-emission-type electron-emitting devices can be arranged on a substrate (rear plate) to constitute an electron source. As in a cathode ray tube (CRT), an display panel can be fabricated by placing a substrate (face plate) that includes a light-emitting member, such as a fluorescent member, which emits light in response to electron beam irradiation, opposite the rear plate and sealing the peripheral space between the face plate and the rear plate.
In a conventional electron-emitting device, heat or another factor generated by sealing or operation (electron emission) may cause La in a LaB6 layer to diffuse into an underlying structure formed of an electroconductive member, or may cause metal elements in the structure to diffuse into the LaB6 layer. Such diffusion may interfere with the function of the low-work-function LaB6 layer, thereby altering the electron emission characteristics of the electron-emitting device.
This situation is more noticeable in a polycrystalline LaB6 layer than in a monocrystalline LaB6 layer. This is possibly because the diffusion of metal elements contained in the structure into the LaB6 layer and the diffusion of La contained in the LaB6 layer into the structure occur through grain boundaries in a polycrystalline layer.